1. Field of the Invention
The present invention relates to a dielectric ceramic composition.
2. Description of the Related Art
In recent years, small devices having good high-frequency properties have been required as electronic devices, such as filters, resonators, and capacitors, used in high-speed large-capacity mobile communication devices such as smartphones. The most commonly used type of such a device is a surface mount device (SMD) including conductors such as electrodes and wires therein (hereinafter, conductors such as electrodes and wires included in high-frequency devices are referred to as “internal conductors”).
To decrease the cost of the devices, it is desirable to use an inexpensive conductor with low resistance, such as Ag, as the internal conductor. Various dielectric ceramic compositions having low-temperature sintering properties that allow Ag having a melting point of 961.9° C. to be used as the internal conductor have been proposed. For example, a dielectric ceramic composition mainly composed of a BaO-rare earth oxide-TiO2-based compound has a high relative permittivity (∈r) and a high Q value, and a resonator or the like formed using such a dielectric ceramic composition has a low resonant frequency temperature coefficient (τf). Thus, such dielectric ceramic compositions are being widely studied.
For example, Japanese Unexamined Patent Application Publication No. 2010-235327 and Japanese Patent No. 3680765 each disclose a dielectric ceramic composition mainly composed of a BaO-rare earth oxide-TiO2-based compound having low-temperature sintering properties so that Ag or an alloy mainly composed of Ag can be used as an internal conductor.
Japanese Unexamined Patent Application Publication No. 2010-235327 discloses a dielectric ceramic composition including a component represented by composition formula {α(xBaO.yNd2O3.zTiO2)+β(2MgO.SiO2)} as a main component and zinc oxide, boron oxide, a glass having a softening point equal to or lower than a certain temperature, and silver as minor components. In the dielectric ceramic composition, the mass ratios of the minor components to the main component are certain mass ratios. Japanese Patent No. 3680765 discloses a dielectric ceramic composition including a BaO—TiO2—ReO3/2-based ceramic composition (Re is a rare-earth element) represented by xBaO-yTiO2-zReO3/2 and a glass composition containing silicon oxide, boron oxide, magnesium oxide, zinc oxide, aluminum oxide, lithium oxide, and an alkaline-earth oxide (at least one of Ba, Sr, and Ca).
However, in the case where an electronic device such as a capacitor is produced using the above-described dielectric ceramic composition including a BaO-rare earth oxide-TiO2-based compound as a main component and zinc oxide and boron oxide as minor components or glass components, if the content of zinc oxide is high, the sintering does not sufficiently proceed due to the zinc oxide having a high melting point and the density after the sintering tends to be low. In addition, it is possible that the zinc oxide does not sufficiently react with other components and thus the elution of unreacted zinc oxide occurs in a process. If the content of boron oxide is high, the elution of boron may occur in a process. If the content of glass is excessively high, the elution of a glass component may occur in a process.
The elution of zinc oxide and boron oxide degrades electrical properties and the power loss in high-frequency devices excessively increases. Therefore, it is difficult to handle a composition having low chemical resistance in a process.